After harvest and storage problems are major dilemma, which requires to be looked into carefully in developing nation like Nigeria. This paper presents a development of low-cost hybrid solar dryer for food preservation with the objective of setting optimum drying parameters for the preservation of cassava and tomato products. The work was carried out by designing, constructing and finally evaluating the hybrid dryer for effective performance. The optimization of the drying parameters was done using composite technique (Response surface method). The assessment of the dryer shows that 150 Kg cassava mesh and 5000 grams of tomato with 35% and 94% moisture content, respectively were dried to 100 Kg and 334 g with 10% moisture level for 4 hours and 11 hours respectively, for cassava and tomato. The optimization result shows that the dryer will perform optimally with drying temperature of 62°C and 48°C for cassava and tomato respectively with 24% and 91% moisture uptake. Therefore, sustainable techniques for preservation of food are essentially required. Hybrid solar dryer is an alternative to consider in the situation.
Drying process is one of the ubiquitous forms of conservation of food items that prolongs the food item’s shelf life. This type of operation is described as concurrent energy and mass transfer where water content is withdrawn from food material via superheated air [
Solar dryers have merits over the conventional sun drying if correctly designed [
Several works were conducted on solar dryer to test the energy efficiency and cost effectiveness using different kinds of foods and vegetables. According to Sharma [
This paper is aimed at developing a low-cost sustainable hybrid solar dryer for vegetables and tubers (tomatoes and cassava) with the objectives of examine the energy efficiency of the dryer in term of drying time of the products and the optimisation of the drying parameters for the dryer.
Study Site
Ogun is a state in south western part of Nigeria created in 1976. It borders Lagos state in south, Oyo and Osun states to the north, Ondo to the east and Republic of Benin to the west. It is located on the map with coordinates 7˚N, 3˚ 35"E with a total population of 3,751,140 (2006b Census). It has land mass of 16,980.55 km2 and total GDP/Capital of $2740 [
A sustainable drying system remains a captious factor for the design and construction of food preservation systems in Nigeria, particularly in the rustic communities. As part of the alms toward ameliorating drying technology in Nigeria, development of a hybrid solar drying system was initiated. The dryer was installed at Olokola Farm in Obafemi-Owode Local Government of Ogun-State, Nigeria purposely for drying of mash cassava tubers for conversion to other products like Laafun or Starch and also other perishable edibles.
The design integrates solar and indirect heating drying apartment. The roof of the constructed drying facility was covered with white thermo plastics and the inside bears trays on an elevated platforms. The dryer utilizes solar energy amid daytime while heat is provided via the apartment in the evening to further drying, if necessary. The heating apartment was constructed with hollow drum fitted from outside. The maximum drying temperature reached was 65˚C with a drying mass rate of 100 - 160 kg wet mash/day and an average final moisture content of 10%. The processors now have advantage of working their products any time with little or no reliance on the use of wood.
Design of the Dryer
The system comprises of four parts, the drying apartment constructed with brickwork scaling 6.8 m in length and width respectively, with four sides without window. The openings with net provide vents (lower and upper) for moisture escape and permits natural air flow in the system. The polycarbonate material serves dual purposes as roof and solar radiator. Two aluminium drums inserted to the back wall and projected into the drying apartment provide means of radiating heat into the apartment. There are two alternatives to consider in placing the products; a rack system or an elevated metal stand. The elevated stand type was chosen due to easy adaptability of the design whereby the surface for drying was designed with stainless steel and angle iron as stands. The surface for drying is twice it degree as energy receptor when the surface is illuminated. Heat is reserved and alienated unto the product to be dried by spreading thinly on it.
Design of the Drying Apartment
The major design considerations of the drying apartment are listed as follow: [
1) Size in mass of product to be dried per batch or day and capacity of the drying cabinet to contain the material.
2) Cubage of the dryer (kg/batch).
3) Method of loading and removing the product.
4) Materials for dryer and tray fabrication.
5) Modality of channeling hot air through the product to be dried.
6) Potent dissemination of hot air through the dryer.
7) Openings as a means of escape of the warm moist air from the drying apartment.
The mass of hot air that is necessary to dry specific mass of the product is determined as follows:
Energy Balance Equation
The energy balance equation expresses the concept as follows:
The energy accessible from the air via the product in the dryer must be the same as energy required to vapourise the moisture content. The withdrawal of moisture from a surface via vapourization demands a measurable heat equitable to the latent heat of vapourization of water plus an amount of air flow over the surface of the product to push away the water vapour released. Therefore, the expectation in solar dryer is to achieve optimum temperature Tf and air flow ma to drive away certain amount of water, mw. Therefore, it is calculated thus:
m w L = ( T F − T ) i m a C p (1)
where mw is the mass of water vapourized, L is the latent heat of vapourization, ma is the mass of air disseminated, Cp is the specific heat capacity of dry air and Tf, Ti are the final and initial temperatures respectively.
Consequently, the volume of air can be determined using gas laws:
V a i r m v = ( m a m v ) ( R T P ) (2)
Therefore, V a i r = m a R T P (3)
where mw, the quantity of water vapourised can be evaluate from moisture ratio scale, or using energy balance equation. Due to the fact that vapour pressure of bound water in hygroscopic material is less than saturation, the impact of bound water is also to be taken into consideration. Also, the value of the vapour pressure must be relatively higher than the latent heat value selected. The expressions are useful in evaluating different parameters as mentioned. For this purpose, these were used in evaluating the mass of air needed for drying tomatoes and mashed cassava tuber products [
The following criteria were taken to consideration in the evaluation of the dryer:
1) Direct technique of trapping solar energy
2) Drying temperature in the range of 50˚C - 70˚C
3) Discretional method of heating
4) Direction of air flow.
An unload examination of the heat gradient of the developmental dryer was carried out on the 15th of January 2016 with temperature condition, warmest (32.2˚C), coldest (22.4˚C) and precipitation (1 mm) The temperature was clocked at the space of 20 minutes interval by means of Hobo data clocking device which was set on the stainless steel drying surface. A maximum temperature of 65˚C was achieved, which was within the limit of design consideration temperature acceptable for drying cassava and some other edible products.
5000 g of fresh tomatoes and 150 kg of pulverized cassava mash with a moisture content of about 94% wet basis and 35% wet basis respectively were packed
Products | Permissible Drying Temperature (˚C) | ||
---|---|---|---|
Initial Moisture (%) | Final Moisture (%) | ||
Maize | 35 | 15 | 60 |
Carrots | 70 | 5 | 75 |
Wheat | 20 | 16 | 50 |
Onions | 80 | 4 | 55 |
Potato | 75 | 13 | 75 |
Fish | 75 | 15 | 50 |
Banana | 80 | 15 | 70 |
Coffee | 50 | 11 | 75 |
Cotton | 50 | 7 | 75 |
Ground nut | 40 | 9 | 30 |
Leather | 50 | 18 | 35 |
Fabrics | 50 | 8 | 75 |
Source: [
into the dryer at 8:05 AM and 12.05 PM respectively, to achieve a targeted 10% moisture content simultaneously (minimum permissible moisture content). The moisture content of the products was measured with a moisture meter at space of time of twenty minutes. The energy utilized for the dryer was gotten from the solar rays and addition heat from the drying chamber. 100 kg dry weight of cassava was weighed after drying time of 4 hours, while 334 g dry weight of tomatoes was weighed after drying time of 11 hours at the targeted moisture content of 10% for both products.
The optimisation of the drying process was done using response surface methodology.
Drying Temp (˚C) | Drying Time (Min) | Mass on Wb (Kg) | mass on Db (Kg) | mass of H2O | % moisture retained | % moisture uptake |
---|---|---|---|---|---|---|
60 | 12:05 | 150.00 | 97.00 | 52.50 | 35.00 | 0.00 |
62 | 12:25 | 146.50 | 97.00 | 49.10 | 32.70 | 2.30 |
62 | 12:45 | 142.00 | 97.00 | 44.50 | 30.40 | 2.30 |
65 | 13:05 | 136.40 | 97.00 | 38.90 | 27.40 | 3.00 |
65 | 13:25 | 130.70 | 97.00 | 33.28 | 24.40 | 3.00 |
65 | 13:45 | 124.80 | 97.00 | 27.59 | 21.10 | 3.30 |
65 | 14:05 | 119.96 | 97.00 | 22.58 | 18.10 | 3.00 |
63 | 14:25 | 115.50 | 97.00 | 18.00 | 15.10 | 3.00 |
64 | 14:45 | 112.60 | 97.00 | 15.00 | 12.60 | 2.50 |
64 | 15:05 | 109.80 | 97.00 | 12.40 | 11.10 | 1.50 |
63 | 15:25 | 109.00 | 97.00 | 12.10 | 10.60 | 0.50 |
64 | 15:45 | 107.00 | 97.00 | 10.90 | 10.20 | 0.40 |
60 | 16:05 | 100.00 | 97.00 | 3.00 | 10.00 | 0.20 |
Drying Temp (˚C) | Drying Time (Min) | Mass on Wb (g) | Mass on Db (g) | Mass of H2O | %moisture retained | %moisture uptake |
---|---|---|---|---|---|---|
31 | 08:05 | 5000.00 | 300.00 | 4700.00 | 94.00 | 0.00 |
31 | 08:25 | 4940.00 | 300.00 | 4640.00 | 92.80 | 1.20 |
33 | 08:45 | 4825.04 | 300.00 | 4525.00 | 91.60 | 1.20 |
34 | 09:05 | 4642.54 | 300.00 | 4342.54 | 90.10 | 1.50 |
36 | 09:25 | 4399.36 | 300.00 | 4099.36 | 88.30 | 1.80 |
36 | 09:45 | 4105.44 | 300.00 | 3805.45 | 86.50 | 1.80 |
40 | 10:05 | 3752.68 | 300.00 | 3452.68 | 84.10 | 2.40 |
42 | 10:25 | 3365.94 | 300.00 | 3065.94 | 81.70 | 2.40 |
43 | 10:45 | 2969.19 | 300.00 | 2669.19 | 79.30 | 2.40 |
48 | 11:05 | 2565.49 | 300.00 | 2265.49 | 76.30 | 3.00 |
52 | 11:25 | 2167.67 | 300.00 | 1867.68 | 72.80 | 3.50 |
55 | 11:45 | 1826.05 | 300.00 | 1526.04 | 70.40 | 2.40 |
60 | 12:05 | 1534.41 | 300.00 | 1234.41 | 67.60 | 2.80 |
62 | 12:25 | 1294.30 | 300.00 | 994.30 | 64.80 | 2.80 |
62 | 12:45 | 1102.46 | 300.00 | 802.47 | 62.00 | 2.80 |
65 | 13:05 | 942.73 | 300.00 | 642.73 | 58.30 | 3.70 |
65 | 13:25 | 814.73 | 300.00 | 514.73 | 54.60 | 3.70 |
65 | 13:45 | 714.70 | 300.00 | 414.70 | 50.90 | 3.70 |
65 | 14:05 | 637.91 | 300.00 | 337.34 | 47.20 | 3.70 |
63 | 14:25 | 583.68 | 300.00 | 283.23 | 44.40 | 2.80 |
64 | 14:45 | 542.81 | 300.00 | 242.81 | 41.60 | 2.80 |
64 | 15:05 | 511.15 | 300.00 | 211.15 | 38.90 | 2.70 |
63 | 15:25 | 486.06 | 300.00 | 186.06 | 36.40 | 2.50 |
---|---|---|---|---|---|---|
64 | 15:45 | 464.77 | 300.00 | 164.77 | 33.90 | 2.50 |
60 | 16:05 | 446.40 | 300.00 | 146.40 | 31.50 | 2.40 |
58 | 16:25 | 429.95 | 300.00 | 129.90 | 29.10 | 2.40 |
55 | 16:45 | 415.22 | 300.00 | 115.23 | 26.80 | 2.30 |
42 | 17:05 | 401.73 | 300.00 | 101.73 | 24.50 | 2.30 |
42 | 17:25 | 389.18 | 300.00 | 89.18 | 22.20 | 2.30 |
40 | 17:45 | 378.62 | 300.00 | 78.62 | 20.20 | 2.00 |
33 | 18:05 | 369.67 | 300.00 | 69.67 | 18.40 | 1.80 |
33 | 18:25 | 361.36 | 300.00 | 61.36 | 16.60 | 1.80 |
34 | 18:45 | 353.84 | 300.00 | 53.84 | 14.90 | 1.70 |
34 | 19:05 | 346.71 | 300.00 | 46.71 | 13.20 | 1.70 |
34 | 19:25 | 339.87 | 300.00 | 39.87 | 11.50 | 1.70 |
34 | 19:45 | 333.99 | 300.00 | 33.99 | 10.00 | 1.50 |
dryer per time. In
In
increase in the drying temperature was observed from 31˚C to 65˚C between 8:05 till 1:05 pm. This was due to the fact that solar energy was gradually been introduced into the drying process. A steady drying temperature was observed at 65˚C for about an hour during the course of the drying process. The drying temperature steadily falls from 65˚C to 34˚C at 2:25 pm down till the end of the drying process at about 7:45 pm. This could be traced to the decrease in solar energy, thus limiting the drying process to the heat from the drying chamber.
Optimisation Results
Drying process parameters were identified as drying temperature, drying time and percentage moisture uptake. The optimization of the drying parameters was carried out to determine the optimum values of the parameters that will yield the best result.
S/N | Parameters | Values |
---|---|---|
1 | Highest Temperature achieved | 65˚C |
2 | Light Illumination Capacity | 90% |
3 | Velocity of Air | 0.1 m/s |
4 | Final Moisture Content | 10% |
5 | Mass of Cassava after Drying | 100 Kg |
6 | Mass of Tomato after Drying | 334 g |
7 | Maximum Loaded Capacity | 250 Kg |
S/N | Optimum Drying | Optimum Drying | Optimum % H20 |
---|---|---|---|
Temperature (˚C) | Time (Min) | Uptake | |
1 | 62.19 | 13.26 | 22.84 |
2 | 63.64 | 15.50 | 21.27 |
3 | 60.21 | 14.23 | 23.43 |
4 | 60.25 | 14.02 | 23.42 |
5 | 64.03 | 15.06 | 21.26 |
6 | 61.28 | 15.25 | 22.42 |
7 | 61.22 | 12.28 | 21.76 |
8 | 62.83 | 14.21 | 22.71 |
9 | 62.87 | 15.18 | 22.04 |
10 | 60.89 | 14.17 | 23.2 |
11 | 62.95 | 13.30 | 22.7 |
12 | 61.61 | 14.46 | 22.81 |
13 | 62.02 | 15.37 | 22.04 |
S/N | Optimum Drying | Optimum Drying | Optimum % H20 |
---|---|---|---|
Temperature (˚C) | Time (Min) | Uptake | |
1 | 42.11 | 10.26 | 90.45 |
2 | 54.07 | 15.25 | 90 |
3 | 32.48 | 19.16 | 87.45 |
4 | 38.98 | 10.36 | 90.07 |
5 | 59.28 | 13.93 | 88.79 |
6 | 56.14 | 16.78 | 88.89 |
7 | 48.77 | 13.40 | 91.13 |
8 | 41.29 | 11.44 | 90.79 |
9 | 57.44 | 14.85 | 89.22 |
10 | 61.62 | 14.78 | 87.73 |
11 | 50.18 | 13.41 | 90.98 |
12 | 61.49 | 17.29 | 86.71 |
13 | 34.65 | 16.46 | 89.41 |
at 13:40 drying time to achieve 91.3% moisture uptake.
Limitations
1) Little or no control on the sources of heat made available in the dryer
2) There is no consistency in the air flow over the product
S/N | Items | Quantity | Unit Cost | Estimated Cost (N) | Estimated Cost ($) |
---|---|---|---|---|---|
1 | Cement | 80 bags | 1500 | 120,000 | 286 |
2 | Transparent Plastic Material (Roof) | 30 | 3000 | 90,000 | 214 |
3 | Moulded Bricks (6 inches) | 100 | 1000 | 100,000 | 238 |
4 | Net | 2 | 200 | 400 | 1 |
5 | Metal Drum | 3 | 10,000 | 30,000 | 71 |
6 | Planks (Softwood, 1 × 12 × 12) | 20 | 1400 | 28,000 | 67 |
7 | Planks for Ceiling) | 20 | 800 | 16,000 | 38 |
8 | Nails | 10,000 | 24 | ||
9 | Stainless Steel | 2 sheets | 50,000 | 100,000 | 238 |
10 | Gravels (25 tons) | 1 | 30,000 | 30,000 | 71 |
11 | Sand (25 tons) | 2 | 15,000 | 30,000 | 71 |
12 | Paint/Accessories | 20,000 | 48 | ||
13 | Labour (Carpenter/Bricklayer) | 50,000 | 119 | ||
14 | Transportation to site | 20,000 | 48 | ||
Total | 644,400 | 1534 |
$1 is equivalent to N420.
Solar system of drying is an encouraging technology for drying of food products for less developed country like Nigeria, where there is abundance in solar energy. This can reduce the post-harvest food spoilage which is a major challenge in the country to a large extent. Despite drying condition varies from one product to another, a dryer may be designed to accommodate different products with good checked of parameters such as temperature and the mass flow rate. The performance evaluation of the case study shows a successful design and an evidence of a worthwhile sustainable technology that should be given mass puffery.
Adefemi, A.O. and Ilesanmi, D.A. (2018) Development and Optimisation of Drying Parameters for Low-Cost Hybrid Solar Dryer Using Response Surface Method. Journal of Sustainable Bioenergy Systems, 8, 23-35. https://doi.org/10.4236/jsbs.2018.82002